linux-kernel - Re: [PATCH v2 2/3] serial: 8250_early: prepare for dynamic BASE

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Message-ID: <54AA8AFC.9020706@hurleysoftware.com>
Date:	Mon, 05 Jan 2015 08:00:44 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	Vineet Gupta <Vineet.Gupta1@...opsys.com>,
	gregkh@...uxfoundation.org
CC:	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
	robh@...nel.org, jslaby@...e.cz, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v2 2/3] serial: 8250_early: prepare for dynamic BASE_BAUD

Hi Vineet,

On 01/05/2015 06:30 AM, Vineet Gupta wrote:
> BASE_BAUD is pain in neck for multi-platform support as it hard codes at
> build time the clk value for early uart.
> 
> Mitigate this by allowing arches/platforms to provide their own version
> which can do dynamic setup based on DT values etc (see next patch for
> usage)
> 
> This was needed for ARC SDP platforms based on 2 different FPGA flows, each
> with a different UART clk value.
> 
> Signed-off-by: Vineet Gupta <vgupta@...opsys.com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Jiri Slaby <jslaby@...e.cz>
> Cc: linux-serial@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Cc: Rob Herring <robh@...nel.org>
> Cc: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/tty/serial/earlycon.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/serial/earlycon.c b/drivers/tty/serial/earlycon.c
> index 64fe25a4285c..bfd3537739e0 100644
> --- a/drivers/tty/serial/earlycon.c
> +++ b/drivers/tty/serial/earlycon.c
> @@ -54,6 +54,15 @@ static void __iomem * __init earlycon_map(unsigned long paddr, size_t size)
>  	return base;
>  }
>  
> +unsigned int __weak __init earlycon_base_baud(char *options)
> +{
> +#ifdef BASE_BAUD
> +	return BASE_BAUD;
> +#else
> +	return 1843200/16;	/* x86 early console */
> +#endif
> +}
> +
>  static int __init parse_options(struct earlycon_device *device,
>  				char *options)
>  {
> @@ -87,7 +96,7 @@ static int __init parse_options(struct earlycon_device *device,
>  		return -EINVAL;
>  	}
>  
> -	port->uartclk = BASE_BAUD * 16;
> +	port->uartclk = earlycon_base_baud(options) * 16;

I don't understand why BASE_BAUD can't be defined by arc as arc_earlycon_base_baud().
Why is the weak binding necessary?

I'm pushing back on this because port initialization (and especially 8250)
is already a ridiculous spiderweb.

Regards,
Peter Hurley

>  	options = strchr(options, ',');
>  	if (options) {
> @@ -156,7 +165,7 @@ int __init of_setup_earlycon(unsigned long addr,
>  
>  	port->iotype = UPIO_MEM;
>  	port->mapbase = addr;
> -	port->uartclk = BASE_BAUD * 16;
> +	port->uartclk = earlycon_base_baud(NULL) * 16;
>  	port->membase = earlycon_map(addr, SZ_4K);
>  
>  	early_console_dev.con->data = &early_console_dev;
> 

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